Three guanine nucleotide-requiring reactions occur upon the ribosome during protein chain growth. Two of these, translocation and aminoacyl-tRNA binding, are required for chain growth and the third, synthesis of guanosine tetra- and penta-phosphate (the "Magic Spot" nucleotides), is apparently responsible for the regulatory coupling of protein and RNA synthesis. These reactions occupy a central position in the translational process and consequently an understanding of their mechanisms and regulation is essential to an understanding of overall gene expression. We propose to examine and explain a number of operationally and conceptually related problems which distinguish these reactions: 1. Enzymology of guanine nucleotide involvement; 2. Protein chemistry of Elongation Factors G, Tu, Ts and the stringency factor; 3. Nature and relationship of ribosomal sites of interaction. 4. Control of factor synthesis and degradation; 5. Modes of inhibitor functions; 6. Recognition of aminoacyl-tRNA by EF-Tu. BIBLIOGRAPHIC REFERENCES: M.S. Rohrbach and J.W. Bodley (1976) "Selective Chemical Modification of E. coli Elongation Factor: N-ethyl-maleimide Modification of a Cysteine Essential for Nucleotide Binding" J. Biol. Chem. 251, 930-933. L. Lin and J.W. Bodley (1976) "Binding Interactions Between Radiolabeled E. coli Elongation Factor G and the Ribosome" J. Biol. Chem. 251, in press.